This invention is in the field of electrochemical processes and apparatus. More specifically, the present invention is directed to the electrochemical synthesis and production of Group IV and V volatile hydrides, and a reactor for carrying out the synthesis. The synthesis and the reactor are designed to more efficiently produce high purity hydrides.
High purity gases are required for semiconductor fabrication and doping. Often these gases are dangerously toxic. Commercial compressed gas cylinders store gas at several thousand pounds per square inch pressure and contain one to ten pounds of gas. Hence, centralized production, transportation and storage of these materials presents a hazard to those working with them.
To avoid these hazards, an apparatus has been developed to provide these dangerous gases to be generated only when they are needed such as, for example, at a chemical vapor deposition reactor in a semiconductor manufacturing plant. For example, W. M. Ayers, in U.S. Pat. Nos. 5,158,656 and 6,080,297, describes an electrochemical apparatus and method for supplying volatile hydrides at the proper pressure for introduction into a chemical vapor deposition reactor. Such processes generate metal hydride gas and hydrogen gas from the corresponding metal cathode by employing a sacrificial anode (i.e., an electrode that corrodes to an oxide) and hydroxide-based electrolytes in an undivided electrochemical cell. Such processes, however, do not operate efficiently due to the uncontrolled formation of solid precipitates that are a byproduct of the electrochemical reaction that occurs within the apparatus. The precipitation of these solids has a negative effect on the overall yield and quality of the electrochemically generated hydride gas.
Porter, in U.S. Pat. No. 4,178,224, discloses an electrochemical method for the synthesis of arsine gas that utilizes a dissolved arsenic salt with an oxygen evolving anode. With this method, however, the arsine concentration was limited to less than 25%. Another limitation of Porter's method was the need to balance pressures and liquid levels in the divided anode and cathode sections of the electrochemical cell. This requires an inert gas supply to the cell.
U.S. Pat. Nos. 5,427,659, and 5,474,659, disclose the electrochemical generation of hydride gases with aqueous electrolytes under conditions that avoid oxygen formation. Although these methods also avoid the formation of solid precipitates, the hydride yield is much lower than desired.
Thus, while efforts have continued to provide effective means for producing and delivering hydride gases, there is still a need in the art to improve the quality and quantity of delivered hydride gas product streams.